To ensure the voltage balance of semiconductor switching elements in a converter valve, it is required to connect a resistor with a rated voltage of thousands of volts in parallel with them. Such a resistor is usually made by using a thick-film resistor in a shape of a flat cuboid with a bottom flat surface thereof tightly attached to a radiator, and is mounted in such a manner of being attached to an upper surface of the radiator and facing away from the ground, or mounted in such a manner of being attached to the lower surface of the radiator and facing toward the ground. Electrode extraction ends are all arranged on the same surface, and mounting wing plates are provided therearound for the convenience of fixation. The mounting wing plates and the resistor body can be reinforced by reinforcing ribs. Due to a large voltage difference and a short distance between the electrodes, an insulating material between the electrodes can be electrically polarized, resulting in that the surface of the insulating material in a particular area is electrically charged. In order to ensure enough insulating power, an insulation surface distance between the electrodes, namely, a creepage distance, needs to be increased.
At present, a common practice is to provide some vertical grooves or isolating walls on an insulating housing on the upper surface of a resistor. For example, the CN Design patent No. CN302578229S discloses a product, and a physical diagram of the product is as shown in FIG. 1, where the creepage distance is equal to a distance between electrodes plus a height of rising and falling of a groove or an isolating wall. Another practice is to extract electrodes a particular length by using high-voltage-resistant insulating wires, so that the creepage distance is equal to a distance between the electrodes plus the lengths of two leads. With regard to the connection of a planar resistor and a mounting wing plate, one or two vertical reinforcing ribs may be typically used for fastening.
The above practices have particular disadvantages. Regarding the first practice, dust and dirt may easily deposit in the groove and at the corners of the isolating wall after long-time running of the resistor, resulting in a decrease in creepage distance, which may affect the safety of the device. In addition, the dust and dirt in a narrow groove may be difficult to clear away completely during maintenance. Regarding the second practice, the use of the leads may result in an increase in overall footprint of the resistor, and due to a fixed wire length, it is inflexible in installation and use. With regard to the connection of the resistor body and a mounting wing plate, dust and dirt may easily deposit in a gap between reinforcing ribs, and corners between the reinforcing ribs and the wing plate and between the reinforcing ribs and the resistor body.